Lepton Flavor Non-Universality in B-meson Decays from a U(2) Flavor Model

TL;DR

This paper proposes a U(2) flavor symmetry model with a Z' boson to explain recent anomalies in B-meson decays, aligning well with current data and predicting testable future signals.

Contribution

It introduces a novel U(2) flavor symmetry framework with a Z' boson to account for lepton flavor non-universality in B-meson decays, consistent with existing constraints.

Findings

Successfully reproduces current B-meson decay anomalies

Predicts new signals for future experiments

Aligns with existing flavor violation constraints

Abstract

We address the recent anomalies in semi-leptonic $B$-meson decays using a model of fermion masses based on the $U(2)$ flavor symmetry. The new contributions to $b \to s \ell \ell$ transitions arise due to a tree-level exchange of a $Z^\prime$ vector boson gauging a $U(1)$ subgroup of the flavor symmetry. They are controlled by a single parameter and are approximately aligned to the Standard Model prediction, with constructive interference in the $e$-channel and destructive interference in the $\mu$-channel. The current experimental data on semi-leptonic $B$-meson decays can be very well reproduced without violating existing constraints from flavor violation in the quark and lepton sectors. Our model will be tested by new measurements of $b \to s \ell \ell$ transitions and also by future electroweak precision tests, direct $Z^\prime$ searches, and $\mu$-$e$ conversion in nuclei.